Rotary regenerative air preheater



June 30, 1959 w. FIRGAU ROTARY REGENERATIVE AIR PREHEATEZR Filed Jui 12,1956 United States Patent ROTARY REGENERATIV E AIR PREHEATER WernerFirgau, Heidelberg-Pfafiengrund, Germany, as-

signor to Svenska Rotor Maskiner Aktiebolag, Nacka, Sweden, acorporation of Sweden Application July 12, 1956, Serial No. 597,440

2 Claims. (CL257-6) This invention relates to a rotary regenerative airpreheater with a rotor subdivided into chambers and a pipe linecontaining a fan for returning the leakage air and the entrapped air tothe main air duct. In known types of air preheater of this kind theintake end of the pipe, with returns to the main air stream the leakageair and the air trapped in the chamber that is about to enter the fluegas duct, is located on the cold side of the preheater and it dischargesinto the flue gas duct on that edge of the cover plate where the sectorchambers filled with flue gas move out of the flue gas duct into aneutral zone before re-entry into the air duct. The point of re-entry ofthis return pipe is on the hot side of the air preheater so that theby-pass'ed air re-enters in concurrent flow with the flue gas. Theprincipal distinguishing feature of the present invention from knowntypes of regenerative preheaters consists in that the reentry opening ofthe return pipe is located on the cold side of the air preheater. Inother words both withdrawal and re-entry of the by-passed air iscompleted on the cold side.

This solution would at first sight appear to be ineffective becausere-entry is eifected against the direction of flow of the flue gasstream and this would require a correspondingly increased power outputof the fan incorporated in the return pipe. However, the presentinvention is based upon a proper appreciation of the fact that thisslight increase in power expenditure becomes acceptable when it is bornein mind, that unlike what happens in the known form of construction, areduction in the temperature of the storage mass by contact with therelatively cool returned air before the storage plates have been able totransfer their heat to the air that is to be heated, is thereby avoided.The improvement in thermal efliciency secured by the present inventionmore than offsets the slight increase in power required for the fan.

To illustrate the principle upon which the invention is based anexemplary form of construction is shown in the drawing with reference towhich the basic structural details of the invention as well as thethermal economy of the novel arrangement will be more particularlydiscussed and explained.

The drawing represents this illustrative form of construction in theform of a development of the peripheral surface of the rotor and of thepaths of the currents, in the plane of the paper.

The rotor 1 which is subdivided into sector chambers by partition walls2 may be assumed to move from right to left, as indicated by the arrow.The neutral zones are covered by plates 3 and 3', 4 and 4', in theconventional manner. The channel in the centre is the flue G whereas theair duct L is shown at either extremity in the development of the rotorsurface. The flue gases stream from below upwardly so that the aircorrmpondingly moves from the top downwardly, as shown by thecorresponding arrows. In the drawing the cold side K of 2,892,616Patented June 30, 195.3

2 the airpreheater is shown at the top, whereas the hot side H is shownat the bottom.

The leakage airas well as the air trappedin the chamberthat is about toenter the. flue is returned through the return pipe 5 which includes afan 6. The direc: tion of flow inthis pipe is also indicated by anarrow.

In the position of the rotor 1 shown in the drawing the sector 7 is justabout to enter the flue G. The leakage air and the air trapped in sector7 are therefore exhausted through the duct 5 which opens alongside theedge. of the cover plate 3, and thus such air is prevented from enteringthe flue G.

The exist opening of the duct 5 is opposite the rotor sector 8; Thislatter sector is about to leave the flue G and to pass through theneutral zone covered by the plates 4. and 4' into the air duct L. Theflue gas con: tained in sector 8 is ejected and replaced by theby-passed air emergi-ngfrom pipe 5. Consequently sector 8 will besubstantially filled with air instead of being'filled with flue gas.when it enters the air-duct.

With reference to the storage plates-inserted intothe sector chambers itwas hitherto customary to arrange them more or less parallel with theperiphery. However, it is also known that they can be disposed radially.Both possibilities are applicable to the present invention. It should besaid, however, that a radial arrangement of the storage plates is to bepreferred in forms of construction embodying the present invention.Radial plates provide a further subdivision of the space in addition tothe division created by the partition walls 2 so that the development ofcurrents parallel with the periphery inside the individual sectorchambers is: thereby prevented. Moreover, the individual subsections oflow height (in practice about 10 mm.) formed by the storage platesimpose a direction upon the currents, which prevents any undesirablemixing of entrapped air and flue gas within the chambers that are to beexhausted and/or refilled. Consequently, the extraction of the air fromchamber 7 and the removal and replacement of gas in chamber 8 tend to becleaner than when the storage plates are mounted parallel with the rotorperiphery. In forms of construction embodying the invention the use ofradially or nearly radially disposed storage plates is therefore thebest available disposition among the various known possible solutions.

Such a subdivision of the rotor sectors into partial spaces to be dealtwith in succession for the purpose of air return may also be effected byproviding a grating with radial or substantially radially disposed barsin front of the end face of the rotor 1, such an arrangement forming thesubject matter of an earlier patent. It is, in any case, practical toprovide such a cover grating irrespective as to how the storage platesare disposed because the unavoidable gap between the return pipe 5 andthe storage mass is. reduced and the direction of flow is moresatisfactorily controlled.

The advantages, gained from the point of view of thermal efliciency,which arise as a result of both the exhaust end and the pressure end ofthe return pipe 5 being on the cold side of the air preheater followfrom the following considerations.

If, as has been customary, the return air which has a temperature in theregion of 100 C. is injected on the hot side of the preheater where thetemperature of the storage plates is about 400 C. the latter will bematerially cooled by the injected air owing to the wide difference inthe respective temperatures. The lower temperature of the storage plateson the hot side therefore materially lowers the temperature to which thehot air current can be heated. On the other hand, if the chambers arefilled with air on the cold side where the temperature of the storageplates is only about 0., there is no cooling efiect, but on the contrarythe plates are slightly heated. The temperature of the storage plates onthe hot side is in practice hardly affected so that the theoreticallymaximum available exit temperature of the heated air current is still atthe stated elevated temperature of 400 C.

The above considerations will show that the application of the principleunderlying the invention permits a substantially better utilisation ofthe heat contained in the flue gases than is the case when the returnpipe 5 dis charges on the hot side of the preheater.

What I claim is:

1. Rotary regenerative heat exchanger for gaseous media comprising arotor having a plurality of sector-like compartments carryingregenerative heat exchange material, a stationary structure comprising acasing for said rotor and end plates having inlet and outlet openingsseparated by angularly related separating portions and providing for aprimary and a secondary passage through said heat exchanger for flow incountercurrent direction of a primary gaseous medium to be heated and asecondary gaseous medium to be cooled of lower pressure than saidprimary medium, respectively, said rotor being located so that saidcompartments traverse said passages successively and move between saidend plates to pass directly from one to the other of said passages, achannel interconnecting the radial edges of the separating portionsdefining said secondary passage on the side of the rotor where saidprimary medium enters and said secondary medium is discharged, saidchannel including a fan for returning to said primary passage leakageprimary medium and primary medium trapped in the compartment that isabout to enter the secondary passage, said channel being arranged todischarge into the compartment that is leaving the secondary passage andto discharge the returned primary medium on the side of the heatexchanger where said primary medium enters and said secondary medium isdischarged.

2. Rotary regenerative heat exchanger as claimed in claim 1, in whichsaid regenerative mass comprises plates mainly radially disposed in therotor.

, References Cited in the file of this patent UNITED STATES PATENTS

